Technical Field
The present disclosure relates to a stress measurement method and system for an optical material. More particularly, the present disclosure relates to a stress measurement method and system that are capable of obtaining precise measurement results and efficient measurement processes by simple hardware architecture.
Description of Related Art
The display industry and the MEMS semiconductor industry are held in high regards today. In those industries, planar optical components such as planar glasses are important components due to their functionalities as substrates or carriers during a manufacturing process. For example, a thin-film transistor array and a color filter both should be manufactured on glass substrates in a display panel manufacturing process. The thin-film transistor array and the color filter may be broken due to a residual stress of the glass substrates or an outer force exerts thereon. Moreover, the residual stress or the outer force may cause the liquid crystal layer be broken or generate non-uniform gaps, thereby producing defects on the display panel. The aforementioned defects are judgment indicators of the display panel qualities.
Furthermore, in the photolithography process of modern MEMS semiconductor manufacturing technology, the photo mask is manufactured by coating patterns on a planar glass. Therefore, the residual stress of the planar glass or the external force generated during the photo mask manufacturing process will cause the non-uniformity of the flatness, geometry and dimension of the mask patterns. Finally, the precision of the MEMS semiconductor manufacturing process will be decreased, and an inefficient or inoperable chip will be produced. From above, it has been known that stresses of the planar optical components (e.g. planar glass) will produce defects of the products in the display industry and the MEMS semiconductor industry. For eliminating the defects, the measurement of the residual stress of the planar optical components is required. Moreover, the measurement of the residual stress of the planar optical component should be performed in time, therefore there is a need to develop a stress measurement method and system that can rapidly and systematically perform the stress analysis.
A photoelasticity method is an efficient method for measuring an internal stress of an object that is transparent and has a temporary birefringence (e.g. a stress of a silicon wafer can be measured by an infrared light). However, the glass material has a low temporary birefringence, and the thickness thereof is thinner with the progress of the manufacturing technology. The flexible display has been a high priority in the development of the display industry. The thickness of the flexible planar glass has been reached to 50 μm thereby resulting the difficulty on measuring the residual stress of the planar glass. The conventional photoelasticity method and photoelasticity instrument have insufficient resolution and accuracy on measuring those low-level residual stresses of the planar glass. A low-level stress measurement instrument produced by the American HINDS Instruments Company can only perform one point stress measurement; if whole-field stresses information are desired, a point-to-point scan should be performed to construct the whole-field stress map. Therefore, the space resolution is low and the measurement time is huge, and it is not favorable for performing rapid measurements online. Moreover, this kind of low-level stress measurement instrument requires large quantities of optical components and electric devices, thereby increasing the implementation costs.
Furthermore, in the modern manufacturing processes of the display panel, TFT arrays and color filters are commonly formed on a surface of the planar glass. Similarly, patterns and reflected metal thin films are commonly formed on a surface of the planar glass when manufacturing the photomask. Therefore, a surface of a glass substrate can have no films, films with partial reflection and partial transmission or films with reflection but without transmission. For example, if a surface of a planar glass sample has reflective films or reflective components, the reflection photoelasticity is an effective stress measurement method. However, the method and instrument of the conventional reflection photoelasticity can only measure the stress on a totally reflective region of the planar glass, it cannot measure the region that has no reflection film or partial reflection film. If the region with no reflection film requires to be measured, a transmission photoelasticity should be used cooperatively. To the region that has partial reflection and partial transmission films, different sub-regions should be separated in accordance with different transmittance and reflectivity, and the different calibration procedures and stress measurements should be performed to individual sub-regions. Therefore, the method and instrument of the conventional reflection photoelasticity are complicated and highly costed. Furthermore, complicated image processing and recognition procedures should also be performed in the conventional stress measurement system, thus it is difficult to be applied on rapid online inspection. Moreover, the resolution and accuracy of the measurement are too low to measure the low-level residual stress of a thin planar glass.